Rating: WARTY!
There is no 'dark voyage', so that's the first problem with this book - or at least there wasn't in the first third of the book which was all I read before I gave up in disgust. There's more than one voyage, but the one I read about was hardly dark, and where I thought it was going to include some good action stuff: spying, infiltration, sabotage, adventure, instead it was largely a boring account of day-to-day activity on a boat, no adventure involved. Yawn. The author seems to somehow be missing the point of what a thriller is supposed to be.
It interested me because it was about this Danish boat captain who was helping the allies in World War Two, and his crew was diverse, including a couple of Germans who hated Hitler as much as the rest of the allies did, but the story-telling and the pacing was uninteresting and tedious respectively, and the story was more about the captain than ever it was about the voyage or the adventure such as it was. I felt completely misled by the book blurb, which I believe is on the publisher, not the author, but the author wrote the story I read and it wasn't up to par, so that's on him, and I can't commend this one based on what I could stand to read of it.